Site-specific investigation levels for PFOS and PFOA in soil

The per- and polyfluoroalkyl substances (PFAS) National Environmental Management Plan (NEMP) provides nationally agreed environmental guideline values for use in site investigations. Leaching, groundwater transport and the contamination of surface water and/or groundwater are key indirect exposure pathways for PFAS. To address these issues, the NEMP designates a perfluorooctane sulfonate (PFOS) soil guideline of 0.14 mg/kg. Environment and Climate Change Canada (ECCC) (2017) derived this guideline using a hydrogeological model. For the development of generic screening levels, the ECCC hydrogeological model incorporates a variety of default input assumptions. The of use of generic screening levels may inaccurately estimate PFAS exposure risks and affect site-specific PFAS management decisions, depending upon the hydrogeologic setting and environmental and human exposure scenarios applicable to an individual area of PFAS contaminated soil. This presentation details the development of site-specific investigation levels (SSILs) for PFOS and perfluorooctanoic acid (PFOA) in soils for a portfolio of land. The SSILs provide a refined site-specific assessment of indirect PFAS risks compared to the NEMP guideline. The aim of the SSILs is to assist the site owner in making more efficient and robust site-specific management decisions of PFAS contaminated soils, by making immediately available the soil concentrations of PFAS that require no further risk assessment or management, no matter where on site the soils are located. (author)